The girl is frequently present in Ming's throne room as an attendant. As well as being required to stand around looking pretty, she is required to pay constant attention to the emperor as a mere nod or flick of the hand may indicate that she is required to sound the gong, which usually acts as a signal for whoever is awaiting an audience with Ming that they are now permitted to enter the room. Knowing Ming's intolerance for failure, the girl presumably does not dare to miss such a signal. It is not known if she is a native of Mongo who has always been loyal to Ming, or whether she is one of the many slaves brought in from worlds Ming has conquered.
Fortunately over time Ming appears to deem the gong surplus to his requirements, and the girl is relieved from the burden of operating it, allowing her to concentrate on just standing around looking pretty.
The Gong Girl was played by actress Vivian Mason, who was to be one of the last survivors of the Flash Gordon film serials, living into the 21st Century.